Methods Of Lowering Wordline Resistance

ABSTRACT

Methods for forming  3 D-NAND devices comprising recessing a poly-Si layer to a depth below a spaced oxide layer. A liner is formed on the spaced oxide layer and not on the recessed poly-Si layer. A metal layer is deposited in the gaps on the liner to form wordlines.

TECHNICAL FIELD

This application claims priority to U.S. Provisional Application No.62/515,533, filed Jun. 5, 2017, the entire disclosure of which is herebyincorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates generally to methods of depositing andprocessing thin films. In particular, the disclosure relates toprocesses for filling trenches in substrates.

BACKGROUND

Semiconductor and electronics processing industries continue to strivefor larger production yields while increasing the uniformity of layersdeposited on substrates having larger surface areas. These same factorsin combination with new materials also provide higher integration ofcircuits per area of the substrate. As circuit integration increases,the need for greater uniformity and process control regarding layerthickness rises. As a result, various technologies have been developedto deposit layers on substrates in a cost-effective manner, whilemaintaining control over the characteristics of the layer.

Gate-first process flow for 3D-NAND manufacturing is of interest due tobenefits in device performance and flexibility. The manufacturingprocess starts with a film stack with alternating SiO₂ and poly-Si (OPstack). Such a stack is patterned to build the memory strings. Awordline slit etch is applied to define the memory arrays and aconformal dielectric layer is deposited to passivate the array. Onemajor disadvantage of this OP stack-based 3D-NAND device is its highwordline resistance which results in large latency in deviceprogramming, reading and erasing. Due to the intrinsic semiconductingfeature of poly-Si, it is very difficult to lower the wordlineresistance to the level of metal lines (such as tungsten wordlines ingate-last process).

Therefore, there is a need in the art for methods for forming wordlinesin 3D-NAND and similar devices with low resistance.

SUMMARY

One or more embodiments of the disclosure are directed to processingmethods comprising providing a substrate surface with a plurality ofspaced oxide layers with gaps between the spaced oxide layers andpoly-Si layers in the gaps between the spaced oxide layers. The poly-Silayer is recessed a depth below a surface of the spaced oxide layers. Aliner is formed on the spaced oxide layers and not on the recessedpoly-Si layer. A metal layer is deposited in the gaps on the liner toform wordlines.

Additional embodiments of the disclosure are directed to processingmethods comprising providing a substrate surface with a plurality ofspaced oxide layers with gaps between the spaced oxide layers andpoly-Si layers in the gaps between the spaced oxide layers. The poly-Silayer is recessed a depth below a surface of the spaced oxide layers. Aliner is formed on the spaced oxide layers and the recessed poly-Silayer. A metal layer is deposited in the gaps on the liner to formwordlines. The liner is etched from the spaced oxide layers.

Further embodiments of the disclosure are directed to processing methodscomprising providing a substrate surface with a plurality of spacedoxide layers with gaps between the spaced oxide layers and poly-Silayers in the gaps between the spaced oxide layers. The poly-Si layer isrecessed to a depth below a surface of the spaced oxide layers. A TiNliner is formed on the spaced oxide layers and not on the recessedpoly-Si layer, the liner having a thickness in the range of about 20 Åto about 50 Å. A tungsten layer is deposited in the gaps on the liner toform wordlines. The tungsten layer is deposited by exposing thesubstrate to a tungsten precursor and a reactant, the tungsten precursorcomprises one or more of WF₆, WCl₆ or WCl₅ and the reactant comprisesH₂.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 shows a cross-sectional view of a 3D-NAND device in accordancewith one or more embodiment of the disclosure; and

FIGS. 2A through 2F show a cross-sectional schematic of a process inaccordance with one or more embodiments of the disclosure;

FIGS. 3A through 3C show a cross-sectional schematic of a process inaccordance with one or more embodiments of the disclosure;

FIGS. 4A and 4B show a cross-sectional schematic of a process inaccordance with one or more embodiments of the disclosure;

FIGS. 5A through 5D show a cross-sectional schematic of a process inaccordance with one or more embodiments of the disclosure; and

FIGS. 6A through 6E show a cross-sectional schematic of a process inaccordance with one or more embodiments of the disclosure.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the disclosure, it isto be understood that the disclosure is not limited to the details ofconstruction or process steps set forth in the following description.The disclosure is capable of other embodiments and of being practiced orbeing carried out in various ways.

A “substrate” as used herein, refers to any substrate or materialsurface formed on a substrate upon which film processing is performedduring a fabrication process. For example, a substrate surface on whichprocessing can be performed include materials such as silicon, siliconoxide, strained silicon, silicon on insulator (SOI), carbon dopedsilicon oxides, amorphous silicon, doped silicon, germanium, galliumarsenide, glass, sapphire, and any other materials such as metals, metalnitrides, metal alloys, and other conductive materials, depending on theapplication. Substrates include, without limitation, semiconductorwafers. Substrates may be exposed to a pretreatment process to polish,etch, reduce, oxidize, hydroxylate, anneal, UV cure, e-beam cure and/orbake the substrate surface. In addition to film processing directly onthe surface of the substrate itself, in the present disclosure, any ofthe film processing steps disclosed may also be performed on anunderlayer formed on the substrate as disclosed in more detail below,and the term “substrate surface” is intended to include such underlayeras the context indicates. Thus for example, where a film/layer orpartial film/layer has been deposited onto a substrate surface, theexposed surface of the newly deposited film/layer becomes the substratesurface.

FIG. 1 illustrates a portion of a 3D-NAND type device. A stack 12 oflayers is formed between a source 10 and drain 11. The stack 12 has aplurality of oxide layers 14 that are spaced apart from each other toform gaps between the oxide layers 14 so that each gap forms a wordlineor shell (or template) for a wordline 19 to be formed. The stack 12 hasa top 13 and sides 15.

The stack 12 can have any suitable number of oxide layers 14 or gaps 16.In some embodiments, there are greater than or equal to about 10, 20,30, 40, 50, 60, 70, 80, 90 or 100 gaps 16 formed in the stack 12 thatcan be used to form an equal number of wordlines 19. The number of thegaps 16 is measured on either side of the memory string 17 that connectsall of the individual oxide layers 14. In some embodiments, the numberof gaps 16 is a multiple of 2. In some embodiments, the number of gapsis equal to 2^(n) where n is any positive integer. In some embodiments,the number of gaps 16 is about 96.

The embodiments illustrated in the Figures show an expanded view ofthree oxide layers and two gaps or wordlines. Those skilled in the artwill understand that these expanded views are simplified for descriptivepurposes. In FIGS. 2A through 2F, a baseline flow path for tungstenreplacement is illustrated. In FIG. 2A, a substrate 100 has a pluralityof spaced oxide layers 110 with poly-Si layers between 120.

In FIG. 2B, the poly-Si layers 120 are recessed using an anisotropicetching process. The poly-Si layers 120 can be recessed a depth D belowthe surface 112 of the oxide layers 110. The depth D can be any suitabledistance less than or equal to the thickness of the oxide layers 110. Insome embodiments, the depth D is in the range of about 10% to about 90%of the thickness of the oxide layer 110. In some embodiments, the depthD is greater than or equal to about 10%, 20%, 30%, 40%, 50%, 60%, 70% or80% of the thickness of the oxide layer 110.

In some embodiments, the recess depth D is substantially the same forall of the poly-Si layers 120. As used in this manner, the term“substantially the same” means that recess depth D of any of the layers120 is in the range of about 80% to about 120% of the average recessdepth D for all of the layers 120. In some embodiments, the recessedpoly-Si layers 120 does not expose the memory string 17 or underlyingsubstrate 100 shown in FIG. 2B.

In some embodiments, recessing the poly-Si layer comprises exposing thelayer to an etchant comprising one or more of HF, CF_(x), HCl, Cl₂, HBr,Br₂, H₂, or combinations thereof. The etchant can be diluted with orco-flowed with an inert gas (e.g., He, Ar, Xe, N₂). In some embodiments,recessing the poly-Si layer comprises a plasma to enhance the etchprocess, the plasma can be ICP, CCP, remote CCP, remote ICP, or remoteplasma source (RPS). Pressure can vary from 0.1 to 100 Torr, and wafertemperature can be from −10 to 650° C.

After recessing the poly-Si layers 120, an optional liner 130 can bedeposited. In some embodiments, a conformal liner 130 is formed on theoxide layers 110 and poly-Si layers 120. The liner 130 can be anysuitable material. In some embodiments, the liner 130 comprises titaniumnitride. In some embodiments, the liner 130 consists essentially oftitanium nitride. As used in this manner, the term “consists essentiallyof titanium nitride” means that the composition of the liner is greaterthan or equal to about 95%, 98% or 99% titanium and nitrogen atoms, onan atomic basis. The thickness of the liner can be any suitablethickness. In some embodiments, the liner has a thickness in the rangeof about 10 Å to about 100 Å, or in the range of about 20 Å to about 50Å. In some embodiments, the liner 130 improves the adhesion of asubsequent metal layer. In some embodiments, the liner 130 blocksfluorine diffusion during metal deposition.

In some embodiments, a TiN liner can be deposited by an ALD process. Forexample, sequential exposure to TiCl₄ and NH₃ plasma can be used in atime-domain ALD process or a spatial ALD process. Pressure can vary from0.1 to 100 Torr, and wafer temperature can be from 300 to 650° C. It canbe processed on single wafer chamber or spatial ALD chamber.

As shown in FIG. 2D, a metal 140 can be deposited and filled into therecessed portions of the poly-Si layer 120. The metal 140 fills the gapsand forms a layer of overburden 145. The overburden 145 is the materialthat is deposited outside of the gaps between the oxide layers 110. Theoverburden can by any suitable thickness depending on the process usedto deposit the metal 140. In some embodiments, the overburden 145 has athickness in the range of about 1 Å to about 1000 Å. In someembodiments, the overburden 145 has a thickness greater than or equal toabout 5 Å, 10 Å, 15 Å, 20 Å, 25 Å, 30 Å, 35 Å, 40 Å, 45 Å or 50 Å.

The metal 140 can be any suitable metal used in wordline applications.In some embodiments, the metal film comprises tungsten. In someembodiments, the metal film excludes tungsten. In some embodiments, themetal film consists essentially of tungsten. As used in this regard, theterm “consists essentially of tungsten” means that the composition ofthe bulk metal film is greater than or equal to about 95%, 98% or 99%tungsten on an atomic basis. The bulk metal film excludes the surfaceportions of the metal 140 that might contact another surface (e.g., theoxide surface) or is open for further processing as these areas may havesome small amount of atomic diffusion with the adjacent material or havesome surface moiety like a hydride termination.

In some embodiments, a conformal tungsten film can be deposited using anALD process. In some embodiments, tungsten deposition comprisessequential exposure to a tungsten precursor and a reactant. In someembodiments, the tungsten precursor comprises one or more of WF₆, WCl₆,WCl₅ or combinations thereof. In some embodiments, the reactantcomprises H₂.

In some embodiments, an area-selective tungsten fill process is used.The area-selective tungsten fill can be similar to a conformal tungstendeposition. Some embodiments use one or more of WF₆, WCl₆, WCl₅ orcombinations thereof as a tungsten precursor. Some embodiments use oneor more of H₂, SiH₄, Si₂H₆, B₂H₆ or combinations thereof as a reducingagent. Pressures can vary from 0.1 to 100 Torr and wafer temperature canvary from 0 to 650° C.

As shown in FIG. 2E, the overburden 145 can be etched away to separatethe wordlines 149. In some embodiments, the etch process comprises aselective etch process that will remove the metal 140 withoutsubstantially affecting the liner 130.

After etching the metal overburden 145, the metal 140 remaining in thegaps between the oxide layers 110 forming wordlines 149 is substantiallyeven with the sides of the stack. As used in this manner, the term“substantially even” means that the wordlines 149 within the gaps arewithin ±1 Å of the side of the stack. In some embodiments, as shown inFIG. 2F, the exposed liner 130 can be removed from the sides of theoxide layers 110.

FIGS. 3A through 3C illustrate another embodiment of the disclosure. Inthis embodiment, FIGS. 3A and 3B are analogous to FIGS. 2A and 2B inwhich the poly-Si layer 120 is recessed a depth from the surface. Afterrecessing the poly-Si layer 120, a metal 140 is formed directly in therecessed area using a selective atomic layer deposition (ALD) process.Tungsten, for example, can be deposited only on the poly-Si layer 120but not on the oxide layer 110.

FIGS. 4A and 4B illustrate another embodiment of the disclosure in whicha metal (e.g., tungsten) is directly filled into the wordline area by aconversion reaction. The poly-Si layer 120 in FIG. 4A can be exposed toa tungsten precursor comprising a tungsten halide compound that reactswith the silicon to form a volatile silylhalide and deposit a metallictungsten layer.

In some embodiments, the tungsten precursor comprises WF₆. In someembodiments, exposure to the tungsten precursor occurs at a temperaturein the range of about 300° C. to about 550° C. and a pressure in therange of about 10 T to about 100 T. The tungsten precursor can beco-flowed with other gases that can be diluent, carrier or inert gases(e.g., argon) or reactive gases (e.g., H₂). In some embodiments, thetungsten precursor is co-flowed with a reactive gas that promotes thereaction of the tungsten precursor with the recessed film.

In some embodiments, substantially all of the poly-Si film is convertedto tungsten. As used in this regard, the term “substantially all” meansgreater than or equal to about 95%, 98% or 99% of the recessed film isconverted to tungsten. The amount of time employed to convertsubstantially all of the film depends on, for example, the temperature,pressure, film composition, film thickness and tungsten precursor. Insome embodiments, 200-300 Å of poly-Si can be converted to tungsten inless than about four minutes at 550° C. and 20 Torr.

FIGS. 5A through 5D illustrate another embodiment of the disclosure. Inthis embodiment, FIGS. 5A and 5B are analogous to FIGS. 2A and 2B inwhich the poly-Si layer 120 is recessed a depth from the surface. Afterrecessing the poly-Si layer 120, an oxide protection liner 130 can beformed within the gaps between the oxide layers 110, as shown in FIG.5C. The metal 140 can then be formed directly in the recessed area, asshown in FIG. 5D.

The oxide protection liner 130 can be deposited by a selective processand/or conformal process. In some embodiments, the liner comprises oneor more of TiN, TiSiN, TiAlN, Al₂O₃ or TaN. The deposition can be aone-step deposition process or a deposition-etch process.

FIGS. 6A through 6E illustrate another embodiment of the disclosure. Inthis embodiments, FIGS. 6A and 6B are analogous to FIGS. 2A and 2B,respectively, in which the poly-Si layer 120 is recessed a depth fromthe surface. After recessing the poly-Si layer 120, a liner 130 isformed on the oxide layers 110 and not on the poly-Si layer 120, asshown in FIG. 6C. The metal 140 can be deposited in the recessed area,as shown in FIG. 6D. The liner 130 can then be removed from the exposedsurface of the oxide layers 120, as shown in FIG. 6E.

According to one or more embodiments, the substrate is subjected toprocessing prior to and/or after forming the layer. This processing canbe performed in the same chamber or in one or more separate processingchambers. In some embodiments, the substrate is moved from the firstchamber to a separate, second chamber for further processing. Thesubstrate can be moved directly from the first chamber to the separateprocessing chamber, or it can be moved from the first chamber to one ormore transfer chambers, and then moved to the separate processingchamber. Accordingly, the processing apparatus may comprise multiplechambers in communication with a transfer station. An apparatus of thissort may be referred to as a “cluster tool” or “clustered system,” andthe like.

Generally, a cluster tool is a modular system comprising multiplechambers which perform various functions including substratecenter-finding and orientation, degassing, annealing, deposition and/oretching. According to one or more embodiments, a cluster tool includesat least a first chamber and a central transfer chamber. The centraltransfer chamber may house a robot that can shuttle substrates betweenand among processing chambers and load lock chambers. The transferchamber is typically maintained at a vacuum condition and provides anintermediate stage for shuttling substrates from one chamber to anotherand/or to a load lock chamber positioned at a front end of the clustertool. Two well-known cluster tools which may be adapted for the presentinvention are the Centura® and the Endura®, both available from AppliedMaterials, Inc., of Santa Clara, Calif. However, the exact arrangementand combination of chambers may be altered for purposes of performingspecific steps of a process as described herein. Other processingchambers which may be used include, but are not limited to, cyclicallayer deposition (CLD), atomic layer deposition (ALD), chemical vapordeposition (CVD), physical vapor deposition (PVD), etch, pre-clean,chemical clean, thermal treatment such as RTP, plasma nitridation,degas, orientation, hydroxylation and other substrate processes. Bycarrying out processes in a chamber on a cluster tool, surfacecontamination of the substrate with atmospheric impurities can beavoided without oxidation prior to depositing a subsequent film.

According to one or more embodiments, the substrate is continuouslyunder vacuum or “load lock” conditions, and is not exposed to ambientair when being moved from one chamber to the next. The transfer chambersare thus under vacuum and are “pumped down” under vacuum pressure. Inertgases may be present in the processing chambers or the transferchambers. In some embodiments, an inert gas is used as a purge gas toremove some or all of the reactants. According to one or moreembodiments, a purge gas is injected at the exit of the depositionchamber to prevent reactants from moving from the deposition chamber tothe transfer chamber and/or additional processing chamber. Thus, theflow of inert gas forms a curtain at the exit of the chamber.

The substrate can be processed in single substrate deposition chambers,where a single substrate is loaded, processed and unloaded beforeanother substrate is processed. The substrate can also be processed in acontinuous manner, similar to a conveyer system, in which multiplesubstrate are individually loaded into a first part of the chamber, movethrough the chamber and are unloaded from a second part of the chamber.The shape of the chamber and associated conveyer system can form astraight path or curved path. Additionally, the processing chamber maybe a carousel in which multiple substrates are moved about a centralaxis and are exposed to deposition, etch, annealing, cleaning, etc.processes throughout the carousel path.

During processing, the substrate can be heated or cooled. Such heatingor cooling can be accomplished by any suitable means including, but notlimited to, changing the temperature of the substrate support andflowing heated or cooled gases to the substrate surface. In someembodiments, the substrate support includes a heater/cooler which can becontrolled to change the substrate temperature conductively. In one ormore embodiments, the gases (either reactive gases or inert gases) beingemployed are heated or cooled to locally change the substratetemperature. In some embodiments, a heater/cooler is positioned withinthe chamber adjacent the substrate surface to convectively change thesubstrate temperature.

The substrate can also be stationary or rotated during processing. Arotating substrate can be rotated continuously or in discreet steps. Forexample, a substrate may be rotated throughout the entire process, orthe substrate can be rotated by a small amount between exposures todifferent reactive or purge gases. Rotating the substrate duringprocessing (either continuously or in steps) may help produce a moreuniform deposition or etch by minimizing the effect of, for example,local variability in gas flow geometries.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the disclosure herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present disclosure without departing from the spiritand scope of the disclosure. Thus, it is intended that the presentdisclosure include modifications and variations that are within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A processing method comprising: providing asubstrate surface with a plurality of spaced oxide layers with gapsbetween the spaced oxide layers and poly-Si layers in the gaps betweenthe spaced oxide layers; recessing the poly-Si layer a depth below asurface of the spaced oxide layers; forming a liner on the spaced oxidelayers and not on the recessed poly-Si layer; and depositing a metallayer in the gaps on the liner to form wordlines.
 2. The method of claim1, wherein the metal layer comprises tungsten.
 3. The method of claim 2,wherein the metal layer consists essentially of tungsten.
 4. The methodof claim 2, wherein depositing the metal layer comprises exposing thesubstrate to a tungsten precursor and a reactant.
 5. The method of claim4, wherein the tungsten precursor comprises one or more of WF₆, WCl₆ orWCl₅ and the reactant comprises H₂.
 6. The method of claim 1, whereinthe liner comprises one or more of TiN, TiSiN, TiAlN, Al₂O₃ or TaN. 7.The method of claim 6, wherein the liner has a thickness in the range ofabout 20 Å to about 50 Å.
 8. The method of claim 6, wherein forming theliner comprises sequential exposure to a titanium precursor and anitrogen reactant.
 9. The method of claim 8, wherein the titaniumprecursor comprises TiCl₄ and the reactant comprises NH₃.
 10. The methodof claim 1, wherein there are greater than 50 wordlines.
 11. The methodof claim 1, wherein recessing the poly-Si layer comprises exposing thesubstrate to an etchant comprising one or more of HF, CF_(x), HCl, Cl₂,HBr, Br₂ or H₂.
 12. The method of claim 11, wherein recessing thepoly-Si layer comprises exposure to a plasma.
 13. The method of claim 1,wherein the metal layer is substantially even with the spaced oxidelayers.
 14. A processing method comprising: providing a substratesurface with a plurality of spaced oxide layers with gaps between thespaced oxide layers and poly-Si layers in the gaps between the spacedoxide layers; recessing the poly-Si layer a depth below a surface of thespaced oxide layers; forming a liner on the spaced oxide layers and therecessed poly-Si layer; depositing a metal layer in the gaps on theliner to form wordlines; etching the liner from the spaced oxide layers.15. The method of claim 14, wherein the metal layer comprises tungsten.16. The method of claim 15, wherein depositing the tungsten metal layercomprises exposing the substrate to a precursor comprising one or moreof WF₆, WCl₆ or WCl₅ and a reactant comprises H₂.
 17. The method ofclaim 15, wherein the liner comprises one or more of TiN, TiSiN, TiAlN,Al₂O₃ or TaN.
 18. The method of claim 17, wherein the liner has athickness in the range of about 20 Å to about 50 Å.
 19. The method ofclaim 14, wherein recessing the poly-Si layer comprises exposing thesubstrate to an etchant comprising one or more of HF, CF_(x), HC, Cl₂,HBr, Br₂ or H₂.
 20. A processing method comprising: providing asubstrate surface with a plurality of spaced oxide layers with gapsbetween the spaced oxide layers and poly-Si layers in the gaps betweenthe spaced oxide layers; recessing the poly-Si layer to a depth below asurface of the spaced oxide layers; forming a TiN liner on the spacedoxide layers and not on the recessed poly-Si layer, the liner having athickness in the range of about 20 Å to about 50 Å; and depositing atungsten layer in the gaps on the liner to form wordlines, depositingthe tungsten layer comprises exposing the substrate to a tungstenprecursor and a reactant, the tungsten precursor comprises one or moreof WF₆, WCl₆ or WCl₅ and the reactant comprises H₂.